(√8 - √15 + √8 + √15)² = ?

Let the expression inside the parenthesis be $$x$$. Then $$x = \sqrt{8 - \sqrt{15}} + \sqrt{8 + \sqrt{15}}$$.

Squaring $$x$$, we get $$x^2 = (8 - \sqrt{15}) + (8 + \sqrt{15}) + 2\sqrt{(8 - \sqrt{15})(8 + \sqrt{15})}$$.

$$x^2 = 16 + 2\sqrt{64 - 15} = 16 + 2\sqrt{49} = 16 + 2(7) = 16 + 14 = 30$$.

Therefore, the answer is 30.